Calculator
Mortgage Repayment Calculator
A true annuity at the selected frequency, drawn over the whole term. Interest-only is shown as a second path, not as a footnote.
Inputs
Frequency
Monthly repayment
$3,593.45
Weekly
$828.69
Fortnightly
$1,657.72
Total interest
$693,640.76
The life of the loan
Owing · repaid · interest
This repayment inside a full deal
The Deal Auditor runs the same loan against duty, rent, the acquisition class and ten years of tax, then measures the result against your criteria.
Payments are true annuities at the selected frequency. Many banks quote fortnightly as half the monthly payment - that pays the loan off faster (it's an extra-repayment strategy; model it in the offset calculator). General information only.
P&I or interest-only: what actually changes
A principal-and-interest loan repays debt from day one. Interest-only defers that: for the IO period you pay only the interest, the balance never falls, and when the period ends the full principal must be repaid over what's left of the term - which is why the post-IO payment is always higher than the P&I payment would have been from the start. On the chart, that's the dashed balance line running flat before diving steeper.
Investors still choose IO for two rational reasons: cash flow during the hold, and the fact that the interest component - the deductible part - stays at its maximum while the balance stays high. Whether that deduction is worth anything to you now depends on your acquisition class under the post-May-2026 negative gearing rules: for a post-reform established purchase, quarantined losses defer the benefit substantially. The full picture - repayments, deductions, regime, and the 10-year outcome - is what the Deal Auditor puts together.
Frequently asked questions
How are mortgage repayments calculated?
A principal-and-interest repayment is the fixed amount that fully repays the loan over the term at the given rate, with interest calculated on the outstanding balance each period. On $600,000 at 5.99% over 30 years that is about $3,593 a month. Early payments are mostly interest; the principal share grows over time - the chart on this page shows exactly that crossover.
Are weekly repayments better than monthly?
Slightly, in two different ways. A true weekly repayment (calculated at the weekly rate, as this page does) pays marginally less lifetime interest because the balance falls a little sooner each week. The bigger effect is the common bank trick of paying half your monthly amount fortnightly - 26 half-payments equals thirteen months of payments a year, which genuinely shortens the loan. That accelerated approach is a form of extra repayment, modelled in our offset calculator.
Should investors use interest-only loans?
Interest-only lowers the payment during the IO period and keeps the loan balance - and therefore the tax-deductible interest - at its maximum, which is why many investors use it. The trade-offs: total interest over the life of the loan is higher, the payment jumps when the IO period ends, and IO rates are often slightly higher. Flip the interest-only toggle to see the exact jump, the lifetime cost, and both paths drawn on the chart.
Is loan interest tax deductible?
For an investment property, the interest component is generally deductible - but since the May 2026 reform, what it can be deducted against depends on your acquisition class. For post-reform established purchases, losses including interest are quarantined to rental income. See our negative gearing calculator for exactly how your deduction behaves.